1. Field of the Invention
The present invention relates to a screw device such as ball screw, roller screw or like, and more particularly, to a screw device having a lubricant applying portion that apply a lubricant to a rolling member rolling groove of a shaft.
2. Related Art
A screw device such as ball screw or roller screw is generally composed of a screw shaft having an outer peripheral surface on which a spiral rolling member rolling groove is formed, a nut having a inner peripheral surface on which a loaded rolling member rolling groove is formed so as to correspond to the rolling member rolling groove formed on the screw shaft, and a number of rolling members such as balls or rollers disposed in a loaded rolling member rolling passage (loaded rolling passage, called hereinlater) composed of the rolling member rolling groove of the screw shaft and the loaded rolling member rolling groove of the nut. In this structure, when the screw shaft is rotated relatively with respect to the nut, the nut is moved linearly with respect to the screw shaft and the rolling members performs a rolling motion in the loaded rolling passage.
A return member, forming a return passage, such as return pipe, deflector or the like is mounted to the nut so as to connect one and the other ends of the loaded rolling passage. The return member acts to scoop up the rolling member such as ball rolling on the loaded rolling passage at one end thereof, guide the ball in the return member and then return the ball to the loaded rolling passage at the other one end thereof. According to such action, the ball rolling in the loaded rolling passage circulates endlessly in a circulation passage composed of the loaded rolling passage and the return member.
A screw device of the structure mentioned above, lubrication is performed by using a lubricant applying member. Such lubricating member comprises a lubricant applying felt for applying lubricant to the screw shaft in contact with it and a lubricant storage chamber for supplying the lubricant to the lubricant applying felt. BY applying the lubricant to the rolling member rolling groove of the screw shaft, frictional force which acts on the surface of the rolling member rolling groove will be reduced or stress applied thereon will be weakened. As a result, usable life time of the screw shaft can be elongated against rolling fatigue.
The screw device of the type mentioned above may be utilized, for example, in place of a hydraulic cylinder device in an injection molding machine or press machine, for example, which is operated under a high load. In such a screw device, a high load is applied in operation and a stroke of the nut with respect to the screw shaft is set to be considerably short. When a high load is applied to such the screw shaft, since frictional force and stress acting on the surface of the rolling member rolling groove becomes large, a phenomenon of flaking, such that the surface of the rolling member rolling groove and the surface of the rolling member peel in form of a scale, likely occurs. And as a result, usable life time will be shortened because of rolling fatigue. In order to obviate such defect, and to improve and elongate the usable life time thereof, it is necessary to apply the lubricant to the rolling member rolling groove by utilizing the lubricating device.
With reference to FIG. 19, in a case that lubricating devices 2, 2 are mounted to both end portions of the nut 1 in the axial direction, the following problems or defects will occur.
That is, when the nut 1 is reciprocated in a stroke of a short range St, the lubricating devices 2, 2 are also reciprocated in the same short stroke. In such case, because the lubricating devices 2, 2 only apply the lubricant to short areas (shown with oblique lines) by lubricant applying felts 3,3 in accordance with the stroke St of the nut 1, there may cause a case that the lubricant do not reach an area (area inside the area shown with oblique lines) in which the rolling member rolls on a rolling member rolling groove 4a. In the case of such fear, oil film cannot be uniformly formed, and as a result, usable life time against the rolling fatigue of the screw device will be shortened.